The present invention relates to apparatus and methods for synchronizing a plurality of tape recording and playback machines, such as video tape recorders and audio tape recorders. The present invention may be used, for example, to synchronize a plurality of video tape recorders together, or to synchronize an audio track to a video track.
Several solutions to the problem of synchronizing a video tape with a sound track or various tracks of sound have been put forward in the past.
The earliest solution was to synchronize various tapes mechanically by use of sprockets and sprocket holes in films
The advent of magnetic tape has made electronic synchronization possible. In an initial recording phase, electronic time codes are recorded on video and audio tapes, on specially designated tracks on each tape. These time codes identify the blocks of information recorded on the tapes, the blocks being known as frames. In a later playback phase, the video and audio tapes are synchronized using the recorded electronic time codes read by separate heads. There is a standard film industry time code called the SMPTE time code which uses a standard encoding method known as the Manchester Code. These coding schemes are well known to those skilled in the art. Their names are included for the convenience of the reader.
In the prior art, during playback, tape machines are coupled together via an individual synchronizing apparatus for each tape machine. Two communications channels are provided. A central controlling device transmits control signals to each tape machine for each tape and receives back a status signal from each tape machine. Furthermore, a preselected master machine transmits a frame number to each tape machine for each frame, thus requiring a separate bus coupling the tape machines together for the frame number code, in addition to a separate control bus, generally a serial bus, which is used for controlling the tape transport. The bus for transmitting the frame number code may be a parallel bus, since a relatively large amount of information must be transmitted in order to identify each frame. Due to bandwidth restrictions, the frame number code cannot be transmitted on the same serial bus as the transport control signals. The central controlling device must also determine the relative locations of the various tape machines to be synchronized and control them accordingly. In a typical commercial application, between two and forty separate tape machines may be used. The communications requirements for large numbers of machines become prohibitive in prior art electronic systems. Accordingly, the prior art systems are limited to a relatively small number of tape machines which can be synchronized unless complex bus systems are provided.
An example of a prior art tape synchronizing device is the STUDER TLS 4000 synchronizer. Other known synchronizing systems are described in U.S. Pat. Nos. 4,210,939, 3,911,488, 4,450,490, 4,214,278, 4,335,401 and 4,322,747. Other systems, which relate to time code reading and tape transport control are shown in U.S. Pat. Nos. 4,232,347, 4,360,843, 3,736,565, 2,702,315, 4,267,564, 4,316,224 and 3,274,574.